This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-000203, filed Jan. 4, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an antenna structure and a mobile terminal having the particular antenna structure, particularly, to an antenna structure adapted for use in, for example, a cellular, mobile or PHS (Personal Handy-Phone System) phone or terminal.
2. Description of the Related Art
Mobile phones or terminals are generally provided in general with an antenna, for receiving a high frequency signal from a radio station and for transmission a high frequency signal to the radio station. The antenna employs, in general, an antenna structure constructed to enable extension and retraction of antenna, and is capable of receiving a high frequency signal in the retracted state.
In the antenna structure, a helical first antenna section having a first contact point section is arranged in the mobile terminal body, and a second antenna section having a second contact point section, connected to the first antenna in the longitudinal direction, is housed extensible in the mobile terminal body. When the second antenna section is housed in the mobile terminal body, the helical section alone of the first antenna protrudes from the mobile terminal body, and the first contact point section of the first antenna is connected to the power supply section, with the result that power is supplied to the first antenna section. Also, when the second antenna section is extended from within the mobile terminal body, the second contact point section of the second antenna section is connected to the second contact point section, with the result that power is supplied to the second antenna section. It follows that a high frequency signal can be transmitted and received between the mobile terminal and the radio station whether the antenna is extended or retracted.
As such an antenna, use is made of a monopole antenna having a length of xcex/4, 3xcex/8 and 5xcex/8, where xcex represents the wavelength of the high frequency signal that is transmitted or received.
On the other hand, proposed as an antenna satisfying the demands in recent years for the broad band width and for high gain is a so-called xe2x80x9cself-resonantxe2x80x9d type antenna, of a length xcex/2. This type of antenna has a radiation directivity equal to that of a xcex/2 dipole antenna, non-directive and a high gain characteristic in a horizontal plane. Thus, the self-resonant type can be applied to a so-called xe2x80x9cviewer typexe2x80x9d mobile terminal on which a large liquid crystal screen is mounted so as to make it possible for the user to transmit and receive data, such as character data, still and moving image data, while observing the liquid crystal screen.
Also, in the self-resonant type antenna, it is impossible to directly connect the power supply point of the antenna to a radio frequency circuit section so as to supply a power to the antenna, because the self-resonant type antenna has high impedance at the bottom end thereof. Thus, the antenna is preferably coupled to the radio frequency circuit section via a matching circuit of weak magnetic field coupling type to reduce the Q factor and to increase the bandwidth. The antenna is more preferably coupled to the radio frequency circuit via a matching circuit of xcex/2 capacitive-coupling type, which has a line of xcex/4. This self-resonant type antenna can realize a characteristics having two resonant points and a more broader bandwidth, which is referred to herein after as a xcex/2 capacitive-coupling antenna.
As a retractable antenna, there is known a bottom helical structure in which a helical antenna as the first antenna is fixed in the housing of the mobile terminal, when the extensible antenna as the second antenna is pulled up from the housing.
A xcex/2 capacitive-coupling antenna having the bottom helical structure is disclosed in U.S. Pat. No. 5,717,409, issued Feb. 10, 1998, Garner et al, which has a configuration as shown in FIG. 1. In the mobile terminal shown in FIG. 1, a radio transmission section 3 is arranged within a terminal body 2. An antenna cap 5C is erected on the terminal body 2, and an antenna element 5D constituting an antenna in the retracted state is spirally arranged in the axial direction of the antenna within the antenna cap 5C. Also, a cylindrical frame 5F having a spiral matching circuit element 5E formed on the circumferential wall is coaxially arranged within the antenna element 5D.
An extensible antenna 5G (movable in the direction denoted by the arrows A and B) when extended, is capable of being housed in the cylindrical frame 5F with a sleeve 5H interposed therebetween. If the antenna 5G is extended from the housing or terminal body 2, the antenna 5G is capacitively coupled with the matching circuit element 5E via a capacitive coupling section 5I of the sleeve 5H. Also, if the antenna 5G is housed in the terminal body 2, the antenna element 5D, not the antenna 5G is capacitively coupled with the matching circuit element 5E.
In the xcex/2 capacitive coupling antenna, however, it is necessary to coaxially mount the antenna element 5D and the matching circuit element 5E, leading to the problem that the construction of the antenna is rendered highly complex.
As described above, the construction of the conventional antenna is highly complex.
An object of the present invention is to provide an antenna structure simple in structure and capable of increasing the bandwidth and increasing the gain, and to provide a mobile terminal equipped with the particular antenna structure.
According to a first aspect of the present invention, there is provided an antenna structure arranged in a mobile terminal having a body including a holding section configured to hold an antenna structure and a mobile terminal circuit section housed in the body, comprising:
a flexible substrate mounted within the holding section;
a meander-shaped antenna pattern formed on the flexible substrate;
a matching circuit element configured to substantially match the impedances of the antenna pattern and a mobile terminal section; and
a capacitive coupling element configured to achieve a capacitive coupling between the antenna pattern and the matching circuit.
According to a second aspect of the present invention, there is provided an antenna structure arranged in a mobile terminal having a body including a holding section configured to hold an antenna structure and a mobile terminal circuit section housed in the body, comprising:
a first antenna element extending substantially linearly;
an antenna support mechanism configured to support the first antenna element, arranged within an antenna holding section, and to permit the first antenna element to be withdrawn from a body of a mobile terminal and to be brought back into the body so as to be housed in the body;
a flexible substrate mounted within the holding section and arranged around the first antenna element withdrawn from the body;
a second antenna pattern formed bent on the flexible substrate;
a matching circuit configured to permit the impedance of the first antenna element to be matched with the impedance of the radio transmission section of the second antenna pattern; and
a capacitive coupling element configured to permit the first antenna element and the second antenna pattern to be coupled with the matching circuit by a capacitive coupling.
According to a third aspect of the present invention, there is provided a mobile terminal, comprising:
a first antenna element extending substantially linearly and having an antenna axis;
a body including a housing section for housing the first antenna element;
an antenna support mechanism configured to support the first antenna element, housed in the housing section, and to permit the first antenna element to be withdrawn from the body of a mobile terminal along the antenna axis and to be brought back into the body along the antenna axis so as to be housed in the body;
a flexible substrate mounted within the housing section and arranged around the first antenna element withdrawn from the body;
a second antenna pattern formed bent on the flexible substrate;
a mobile terminal circuit mounted within the body and configured to receive and transmit a mobile terminal signal through the first antenna element and the second antenna pattern;
a matching circuit element configured to permit the impedance of the first antenna element to be matched with the impedance of the mobile terminal circuit section of the second antenna pattern; and
a capacitive coupling element configured to permit the first antenna element and the second antenna pattern to be coupled with the matching circuit by a capacitive coupling.
Further, according to a fourth aspect of the present invention, there is provided a mobile terminal, comprising:
a flexible substrate;
a body including a housing section for housing the flexible substrate, the housing section protruding from the body along a first reference axis;
an antenna pattern formed bent on the flexible substrate, the antenna pattern extending in a meandering fashion along a second reference axis, and the first and second reference axes forming an angle falling within a range of between 45xc2x0 and 90xc2x0;
a mobile terminal circuit housed in the body and configured to receive and transmit a mobile terminal signal through the antenna pattern;
a matching circuit element configured to permit the impedance of the antenna pattern to be matched with the impedance of the mobile terminal circuit section; and
a capacitive coupling element configured to permit the second antenna pattern to be coupled with the matching circuit by a capacitive coupling.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.